This invention relates to copolyamides of hexamethylene terephthalamide (6TA) and hexamethylene isophthalamide (6IA) and more particularly to hollow, biaxially oriented, optically clear articles formed of such copolyamides.
Containers formed of thermoplastic barrier polymers for packaging environmentally sensitive food and highly permeable non-food products are known. Barrier polymers are materials possessing significant resistance to permeation of one or more fluids such as oxygen, and carbon dioxide gas, water vapor, hydrocarbons and organic solvents and the like. Products which have been packaged, or are potentially packagable, in articles formed of barrier polymers include carbonated soft drinks, beer, salad oils, nuts, jams, coffee, medicines, household chemicals, agricultural fluids, cleaning solvents, industrial adhesives, and the like. Particularly demanding food packaging applications are those required to accommodate hot fill (90.degree.-100.degree. C.) and autoclave (125.degree. C.) temperatures for sterilization, such as encountered with baby foods, canned goods and the like. Barrier polymers molded into containers such as bottles, cans and like shapes which have been used in these applications include acrylonitrile copolymers containing more than 50 weight percent acrylonitrile, biaxially oriented chemically modified and unmodified polyethylene terephthalate and high density polyethylene surface treated with fluorine. Laminates of plural layers with a barrier polymer such as vinylidene chloride or ethylene vinyl alcohol as one layer have also been used.
In spite of progress to date, there remains a desire in the marketplace for cost-effective barrier polymer packages having an improved balance of properties including optical clarity, strength, solvent and gas barrier resistance and, in the case of foods, the capability to withstand high temperatures.
Japanese (laid-open) patent application No. 79472/76 of Toray Industries, Inc. recognizes copolyamides of hexamethylene terephthalamide (hereinafter referrerd to as "6TA") (20-65 weight %) and hexamethylene isophthalamide (hereinafter referred to as "6IA") (35-55 weight %), optionally including epsilon caprolactam, in the form of biaxially stretched packaging film having superior oxygen, water vapor, etc. gas barrier properties and resistance to boiling water and high retort temperatures. This publication, however, teaches such copolyamides only as thin, wrapping films having a thickness of about 0.7-0.8 mils (0.017-0.020 mm) initially formed by depositing and solidifying the melt on a casting drum.
U S. Pat. No. 4,022,756 discloses such copolyamides as molecularly oriented fibers.